Pavement markers have become widely accepted as permanent installations for providing visible signals which mark traffic lanes and control the flow of traffic on roadways in connection with, or in place of, conventional painted traffic lines. A large number of such markers employ reflectors which retroreflect light emanating from oncoming vehicles to provide a visible signal to the operators of such oncoming vehicles.
A pavement marker of the type depicted in U.S. Pat. No. 4,195,945 and assigned to applicants' assignee, has generally been manufactured in two different versions. The first has a pavement to top of marker height of 0.41 inch high, and is known as a Stimsonite model '96. The second has a pavement to top of marker height of 0.25 inch, and is known as a Stimsonite model '96 LP. The model '96 has an outside ramp angle of 6.degree., while the model '96LP has an outside ramp angle of 4.degree. . The reduced height of the model '96LP, even though using the same "Model '944" retroreflector, results in approximately 40% of the reflector element being shielded by the road, and thus the retroreflected signal from the 96LP is not as great as the signal from the model '96.
While both models have operated satisfactorily and have been commercially successful, the '96 LP has been utilized in those states where there tends to be either higher speed plowing or much higher traffic volume and its lower height than the model '96 permits less jolting of the operator, particularly during such high speed plow operations as found in expressways in certain parts of the country where there is extremely heavy snowfall conditions.
Exemplary of other snowplowable pavement markers previously known are those disclosed in U.S. Pat. No. 3,790,293 issued to S. A. Heenan et al. on Feb. 5, 1974 and U.S. Pat. No. 3,809,487 issued to R. M. Flanagan on May 7, 1974, both of which are likewise commonly assigned herewith; as well as U.S. Pat. No. 1,952,942 issued to D. E. Ross on Mar. 27, 1934 and U.S. Pat. No. 2,260,498 issued to L. M. Wise on Oct. 28, 1941. Other pavement markers are disclosed in U.S. Pat. Nos. 1,910,791; 1,927,756; 1,952,943; 2,126,224; 2,337,793; 3,332,327; 3,516,337; 3,540,282; 3,587,416; 3,758,191; 3,784,279; 3,975,108 and 3,980,410.
In some areas in which heavier snows occur the plow operators also may tend to adjust the plow blade relative to the longitudinal axis of the roadway, to an angle which may allow the tip of the plow blade to cut away or damage the reflector, or may increase the plow angle such that the plow blade, even though straddling both casting rails or ramps, can drop below the ramps sufficiently to contact the retroreflector and thus damage it. In particular, when the blade angle is greater than 30.degree. with a line perpendicular to the direction of vehicle travel, the blade, and especially the tip of the blade, can enter between the ramps and cause damage to the reflector positioned therein. It is therefore desirable to have a one-way snowplowable pavement marker that will withstand the cutting and abrasive action of snowplow blades set at angles as high as 60.degree. with a line perpendicular to the direction of vehicle travel.
In the '945 patent, snowplowable monodirectional and bidirectional pavement markers are disclosed which include a metal base member having two arcuate-bottom keel members interconnected by an arcuate-bottom support member. The upper surfaces of the keel members respectively define inclined ramps from a plane at one end of the base member toward the other end thereof to corresponding coplanar top surfaces. The support member has a support surface lying below the plane for supporting thereon a retroreflector which is partially recessed below the plane. The keel members and the support member are respectively secured in complementary arcuate recesses with the plane of the retroreflector support surface substantially coplanar with the roadway surface.
In designing these prior art snowplowable pavement markers, it has been a continuing problem to reduce the overall height of the reflector associated with the pavement marker to a minimum level above the roadway surface without undesirable reduction of the retroreflectance of the marker and, accordingly, the visibility of the marker. For example, in attempts to achieve low profile marker designs heretofore, it has been recognized that the angle between the roadway surface and the inclined ramps of the base member should be minimized to reduce the impact of the plow blade on that portion of the housing or casting projecting above the roadway. However, although the ramp angle theoretically could be reduced as low as desired, the lower the angle, the longer the ramp would have to be to maintain the same maximum height and, accordingly, the longer the keel members and the longer the grooves or recesses that would have to be cut in the pavement. The longer the grooves, the greater the time and expense required to form the grooves. Furthermore, the longer the base member, the heavier and more expensive it is. Thus, these factors have served practically to limit to no lower than 6.degree. the outside ramp angle (6.5.degree. inside ramp angle) that could be practically achieved in a prior art bidirectional marker with the full retroreflective area of the existing retroreflectors operatively exposed.
In further attempting to minimize the overall height of the markers above the roadway, it has been suggested in the prior art to further recess the retroreflector elements below the level of the roadway surface. However, in so doing, it has been found that the retroreflectivity and, therefore, the visibility of the marker from a distance can be seriously impaired due to shadowing caused by the lower silhouette of the embedded devices. Partially recessing the reflector elements reduces visibility only if the lowest unshadowed ray from an approaching headlight after refraction at the obverse face strikes the retroreflective element above the lowest point of the cube corner.
Another problem which has been recognized in the design of snowplowable markers is the need to provide devices having improved impact and compression resistance of the retroreflector. In this regard, the development of highly durable devices which would withstand high speed vehicular impact as well as the stress of heavy and frequent plowing has been a primary objective of these devices. A further problem in the design of these products has been the need to provide devices which enable improved tire wiping action to be exerted over the surface of the retroreflector to clean such surface and improve the retroreflectivity thereof without adversely impacting the longevity of the products.
The present invention provides such a one-way snowplowable pavement marker for accommodating snowplow blades set at angles up to 60.degree. with a line perpendicular to the direction of vehicle travel. It has spaced apart primary ramps joined by an arcuatebottom body portion having a front and a rear. A reflector is adhesively mounted toward the rear of the body portion between the primary ramps. An auxiliary ramp is centrally positioned on the front of the body portion between the spaced apart primary ramps to support a snowplow blade when the blade tip is located between the primary ramps. A shelf is formed at the rear of the body portion behind the reflector, the shelf having a height at least equal to the height of the reflector for supporting the snowplow blade tip after it clears the end of the auxiliary ramp with the snowplow blade set at angles up to 60.degree. with a line perpendicular to the direction of vehicle travel. Thus when the tip of the blade first enters the space between the primary ramps, it is supported by the auxiliary ramp. Before the blade leaves the auxiliary ramp it is picked up by the cast-in-place shelf at the rear of the marker thus eliminating contact of the snowplow blade tip with the reflector.
The primary ramps and the auxiliary ramp have a 3.5.degree. ramp angle to reduce ramp blade forces. The primary ramps of the marker casting is fitted with two recesses, one on the interior side of each of the primary ramps. The reflector has a projection on each side and the opposed recesses on the interior side of each of the primary ramps receives a corresponding one of the projections. The projections absorb all shear forces generated by contact of the snowplow blade with the casting so that the adhesive bonding of the reflector to the body portion has to resist only vertical forces.
Further, the novel pavement marker allows wiping and cleaning of the reflector because the distance between the end of the auxiliary ramp and the reflector and the incorporation of a deep radiused pocket therein allows a vehicle tire to touch the reflector as it passes over it, thus wiping and cleaning the reflector. Four bosses support the casting for correct pavement installation. The overall length of the casting is 10 inches so that it can be cast using a Disamatic sand molding machine for high production.
Thus it is an object of the present invention to provide a one-way snowplowable pavement marker for accommodating a snowplow blade set at angles up to 60.degree. with a line perpendicular to the direction of vehicle travel and that will withstand the cutting and abrasive action of snowplow blades set a these angles.
It is also an object of the present invention to provide a one-way snowplowable pavement marker that has an auxiliary ramp positioned between the two primary ramps to support the snowplow blade when the snowplow blade tip enters and is located between the two primary ramps.
It is a further object of the present invention to provide a cast-in-place shelf at the rear of the pavement marker for supporting the blade tip before it clears the end of the auxiliary ramp thereby eliminating contact of the blade tip with the reflector.
It is still another object of the present invention to provide the casting with a recess on the interior of each side of the spaced primary ramps for receiving corresponding projections on the reflector such that the projections absorb all shear forces generated by the snowplowing so that adhesive bonding of the reflector to the casting has to resist only vertical forces which are minimal.
It is also an object of the present invention to provide a pavement marker designed to allow wiping and cleaning of the reflector because of the distance between the end of the auxiliary ramp and the reflector and the incorporation of a deep radiused pocket between the auxiliary ramp and the reflector that allows a vehicle tire to touch the reflector as it passes over it.
It is a further object of the invention to provide a one-way snowplowable pavement marker that incorporates low primary ramp angles of 3.5.degree. to reduce ramp blade forces combined with an auxiliary ramp to allow use of plow blade angles up to 60.degree. with a line perpendicular to the direction of vehicle travel.